[petsc-users] GAMG parameters for ideal coarsening ratio

[Sajid Ali]

 Hi Mark/Jed,

The problem I'm solving is scalar helmholtz in 2D, (u_t = A*u_xx + A*u_yy +
F_t*u, with the familiar 5 point central difference as the derivative
approximation, I'm also attaching the result of -info | grep GAMG if that
helps). My goal is to get weak and strong scaling results for the FD solver
(leading me to double check all my parameters). I ran the sweep again as
Mark suggested and it looks like my base params were close to optimal (
negative threshold and 10 levels of squaring with gmres/jacobi smoothers
(chebyshev/sor is slower)).

[image: image.png]

While I think that the base parameters should work well for strong scaling,
do I have to modify any of my parameters for a weak scaling run ? Does GAMG
automatically increase the number of mg-levels as grid size increases or is
it upon the user to do that ?

@Mark : Is there a GAMG implementation paper I should cite ? I've already
added a citation for the Comput. Mech. (2007) 39: 497–507 as a reference
for the general idea of applying agglomeration type multigrid
preconditioning to helmholtz operators.


Thank You,
Sajid Ali | PhD Candidate
Applied Physics
Northwestern University
s-sajid-ali.github.io
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20200317/c925b3e5/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 86644 bytes
Desc: not available
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20200317/c925b3e5/attachment-0001.png>